<template>
  <ul class="list">
    <li class="item"  
    v-for="item of letters" 
    :key="item" @click="setAlohabet"  
    @touchstart.prevent="handleTouchStart"
    @touchmove="handleTouchMove"
    @touchEnd="handleTouchEnd" 
    :ref="item">{{item}}</li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlohabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      timer: null
    }
  },
  methods: {
    setAlohabet: function (e) {
      // console.log(e.target.innerText)
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const startY = this.$refs['A'][0].offsetTop //A距离顶部的距离
          const touchY = e.touches[0].clientY-79 // 手指距离header下边缘的的距离
          const index = Math.floor((touchY - startY) / 20) // 滑动了第几个字母 
          if(index>=0 && index<this.letters.length){
            this.$emit('change', this.letters[index])
          }
        },16)
        // console.log(index)
        // console.log(e.touches[0].clientY)
        // console.log(startY)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  },
  computed: {
    letters () {
      const letters = []
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  }
}
</script>

<style lang='stylus' scoped>
@import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    right: 0
    top: 1.58rem
    bottom: 0
    width .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
